Mariner 2 observations of the solar wind: 2. Relation of plasma properties to the magnetic field

Abstract

This paper summarizes some of the relations between the interplanetary magnetic field and the positive-ion component of the solar wind as observed by Mariner 2. Both the field strength and plasma density were generally much greater than normal at the leading edge of a long-lived high-velocity stream. For most of the period of observation, the ratio of magnetic energy density to the energy density of thermal motions of the positive ions was of the order of unity. The Alfven velocity was usually in the range 30–100 km/sec, and, during this period, the solar-wind flow past the earth was always greater than the phase velocity of hydromagnetic waves, a necessary condition for the existence of a hydromagnetic bow shock. The Mariner 2 spectrometer, which always faced the sun, measured the proton velocity dispersion, or temperature, along the solar radius vector. The dependence of this temperature on the instantaneous direction of the magnetic field was inconsistent with the condition T∥ > T⊥ observed by the spherical plasma spectrometers on Pioneer 6 and Vela 3, unless the plasma was much hotter when the interplanetary field was perpendicular than when the field was parallel to the solar radius vector.